Author Topic: EEVblog 1385 - 8kW Home Solar Power System EXPANSION  (Read 3761 times)

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Offline Dread

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Re: EEVblog 1385 - 8kW Home Solar Power System EXPANSION
« Reply #25 on: April 04, 2021, 07:59:41 pm »

And as far as redundancy/reliability issues go, there's a plenty of experience to rely on.  You can talk of heated capacitors all you like, but DC-string inverters have typically had a disturbingly high failure rate compared to even old micros.  Read the warranty terms of each if you want to know the manufacturers take on that. And with DC optimization, the optimizer is in same place as the micro, so where's your advantage?

Not when compared to SMA inverters!  As for warranty it's 5 years vs 10 Years with SMA.  Also they will ship you a new one right away if your on their monitoring system.  Keep in mind Dave got that Enphase systems as a promotional item.  I would imagine that after 8 years of great service from SMA if he had to have made a purchase out of pocket it might have been different.  I would not pass up the Enphase offer either but for us on the outside who have to spend lots of $$$ it's not so easy of a decision.
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Offline nctnico

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Re: EEVblog 1385 - 8kW Home Solar Power System EXPANSION
« Reply #26 on: April 04, 2021, 08:19:22 pm »
One thing that all three of the companies suggest I stayed away from was MicroInverters.  The reasoning was always the same, they said that the Inverter was the most likely part to burn out and it's better to deal with a single Inverter than 20 of them. They also said they get extremely hot and therefore have a short lifespan. I mentioned shading and one guy replied that the panels would be set in three per series and that should eliminate most of the problems but if they still encounter a problem they would use Optimizes on the affected panels.    I don't know enough about solar equipment to comment but when three different companies stare you away from something it's a done deal in my head.
It could be none of them has experience with them. But to me it seems micro-inverters don't bring much to the table. They are installed in the worst place (on a hot roof) and instead of high voltage DC you now need to bring high voltage AC to the roof running at higher currents as well. IIRC the typical voltage a DC system runs at is 300V to 400V per string and for a >2000W installation you end up with several strings which each run with relatively low corrents (couple of amps). With all the panels disconnected you bring the voltages on the wiring down to safe levels (unless ofcourse you have panels with very high voltages but I have not seen those myself).

In the end it is all about TCO / ROI. Getting a few % extra might not be worth the extra money. If you install a cheap inverter in a cool place then it is not likely do develop problems due to temperature related aging. Maybe it is even cheaper to have a spare inverter on hand compared to buying a very expensive one and pay for warranty on top.
« Last Edit: April 04, 2021, 08:45:54 pm by nctnico »
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Online bdunham7

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Re: EEVblog 1385 - 8kW Home Solar Power System EXPANSION
« Reply #27 on: April 04, 2021, 08:55:19 pm »
It could be none of them has experience with them.

Or maybe they do!  Enphase had an earlier model with pretty high failure rates and they didn't respond in the best way at first.  Eventually they came out with and replacement/upgrade program.  If I had to make dozens of warranty service calls and go up and replace those for little or no compensation, I might not be so happy either.  HVDC inverters had pretty high failure rates too, but typically only once or twice.

Quote
high voltage DC you now need to bring high voltage AC to the roof running at higher currents as well.

Not really a good comparison.  The AC is just standard wiring protected by a breaker and has no unusual hazards.  Older string systems had HVDC not so well protected, I'll leave it for others to argue that current string systems have reduced hazards.  DC currents are 8-10 amps per string, on Enphase the AC currents are 16 amps maximum per branch.  I've not seen or heard of a fire caused by an Enphase installation.
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Offline nctnico

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Re: EEVblog 1385 - 8kW Home Solar Power System EXPANSION
« Reply #28 on: April 08, 2021, 07:57:38 am »
high voltage DC you now need to bring high voltage AC to the roof running at higher currents as well.

Not really a good comparison.  The AC is just standard wiring protected by a breaker and has no unusual hazards.  Older string systems had HVDC not so well protected, I'll leave it for others to argue that current string systems have reduced hazards.
IMHO this is more of a lack of regulations issue for HVDC wiring in general. Lower current = less energy available = less chance of fire. AC power packs quite a punch due to the energy the grid can provide.
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Offline tszaboo

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Re: EEVblog 1385 - 8kW Home Solar Power System EXPANSION
« Reply #29 on: April 08, 2021, 08:01:22 am »
And as far as redundancy/reliability issues go, there's a plenty of experience to rely on.  You can talk of heated capacitors all you like, but DC-string inverters have typically had a disturbingly high failure rate compared to even old micros.  Read the warranty terms of each if you want to know the manufacturers take on that. And with DC optimization, the optimizer is in same place as the micro, so where's your advantage?

Solaredge optimizers dont have electrolytic capacitors in them, they are ceramic. I guess I dont have to go into the details, that electrolytic capacitors have a life expectancy on the datasheet. Also as I understand the marketing, its 1/3 the component count.

Why is it very different and when does it matter?
In summer, the sun is shining, there is shading on a panel. Say, you have 10 panels, 350W each. Say all systems will have 20% overprovision.
The DC system with optimizer will output 80% of its nominal (DC) nameplate capacity, the maximum of the system.
The Enphase will output about 74%, because 9 panel will output 80% and one 20%.
A regular inverter with two strings will output 60%, as 5 panels will be 100% and the other five 20%

Honestly, beyond the technical discussions, I dont like Enphase because of the bad moves they were pulling in the past. People report that they are charged a monthly fee per panel for the monitoring. And they were charged money, when they were transferring the warranty when selling the house. Even if this only happened in the past, I just dont want to deal with a company that des these things.
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Online Brumby

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Re: EEVblog 1385 - 8kW Home Solar Power System EXPANSION
« Reply #30 on: April 08, 2021, 12:24:07 pm »
:palm:  Did you understand that page?  Did you even READ it?
Not really, I have better things to do with my time, than figuring out what the warranty is somewhere else.
Then DON'T make statements from a position of ignorance!
 

Offline floobydust

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Re: EEVblog 1385 - 8kW Home Solar Power System EXPANSION
« Reply #31 on: April 08, 2021, 09:27:41 pm »
I don't know the exact installation details, but I started with my usual EE first question: "where's the fuse?"
Because the micro-inverters' outputs are all in parallel, I think on the Q-Cable 20A branch max., I wondered if this was covered.
What stops a bank of micro-inverters from roasting a failed one also on that AC bus? There's no local disconnect or fuse that I can see.
Fault LED is a "DC Resistance Low, Power OFF" doesn't make sense on what that is. What power is off, grid or PV and who's got the ohmmeter lol.
 

Offline mikeselectricstuff

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Re: EEVblog 1385 - 8kW Home Solar Power System EXPANSION
« Reply #32 on: April 08, 2021, 09:36:32 pm »

What stops a bank of micro-inverters from roasting a failed one also on that AC bus? There's no local disconnect or fuse that I can see.

I would be highly surprised if they didn't have  an internal fuse as a last-ditch protection measure- as it's potted, any internal fault would be unrepairable so the fuse doesn't need to be replaceable. 
In normal operation they will be actively monitoring everything throughout the AC cycle, so will be able to shut down in the event of any abnormal situation.
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Offline aqarwaen

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Re: EEVblog 1385 - 8kW Home Solar Power System EXPANSION
« Reply #33 on: April 08, 2021, 10:27:49 pm »
DAVE have you actualy tested how much load your solar power system can produce in peak time,before you need to draw extra power from grid?
 

Online bdunham7

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Re: EEVblog 1385 - 8kW Home Solar Power System EXPANSION
« Reply #34 on: April 08, 2021, 11:29:02 pm »
What stops a bank of micro-inverters from roasting a failed one also on that AC bus? There's no local disconnect or fuse that I can see.
Fault LED is a "DC Resistance Low, Power OFF" doesn't make sense on what that is. What power is off, grid or PV and who's got the ohmmeter lol.

If the breaker blows, the inverters all stop working instantly because the grid power goes away.  This is an extremely reliable intrinsic function of the microinverter and is required for anti-islanding certification.
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Online bdunham7

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Re: EEVblog 1385 - 8kW Home Solar Power System EXPANSION
« Reply #35 on: April 08, 2021, 11:38:56 pm »
In summer, the sun is shining, there is shading on a panel. Say, you have 10 panels, 350W each. Say all systems will have 20% overprovision.
The DC system with optimizer will output 80% of its nominal (DC) nameplate capacity, the maximum of the system.
The Enphase will output about 74%, because 9 panel will output 80% and one 20%.
A regular inverter with two strings will output 60%, as 5 panels will be 100% and the other five 20%

Honestly, beyond the technical discussions, I dont like Enphase because of the bad moves they were pulling in the past. People report that they are charged a monthly fee per panel for the monitoring. And they were charged money, when they were transferring the warranty when selling the house. Even if this only happened in the past, I just dont want to deal with a company that des these things.

OK, if you are comparing a Solaredge optimized system with microinverter system, I'll agree that they are similar in efficiency.  Your example pencils out, but it would be an unusual--but not unthinkable--circumstance.  The effect on overall system productivity would still be minimal because that situation will only last for as long a the non-shaded panels can put out near 90% of their rating. 

Your other point about Enphase is entirely true, unfortunately.  I use 'Enphase' and 'microinverter' interchangeably because they dominate the market now, but in the not-too-distant past they were struggling in many ways--high failure rate with a parts-replacement only warranty,  borderline deceptive advertising (I bought mine thinking they were US-made), various attempts at recurring revenue (monitoring, warranty, etc) and more.  I was worried they would go under and I'd have no warranty.  The company has greatly improved under new management, but if I was the one that had been burned by them, I'd not like them either.
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Offline ssander

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Re: EEVblog 1385 - 8kW Home Solar Power System EXPANSION
« Reply #36 on: April 09, 2021, 03:57:17 am »
After Dave's live stream last night. I was wondering about the specific microinverters used.

Enphase also makes an IQ7A inverter and I found this document on their website.

Technical Brief: https://enphase.com/sites/default/files/downloads/support/IQ7A_Vs_IQ7plus_in_Australia.pdf

I'm no expert on the subject, but (there is always a but) it seems to me that the system is correctly spec'd. 
 

Offline EEVblog

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Re: EEVblog 1385 - 8kW Home Solar Power System EXPANSION
« Reply #37 on: April 09, 2021, 05:48:11 am »
After Dave's live stream last night. I was wondering about the specific microinverters used.

Enphase also makes an IQ7A inverter and I found this document on their website.

Technical Brief: https://enphase.com/sites/default/files/downloads/support/IQ7A_Vs_IQ7plus_in_Australia.pdf

I'm no expert on the subject, but (there is always a but) it seems to me that the system is correctly spec'd.

According to them, yes. But they have also admitted that my system will clip on high solar insolation days. Even the 340W output IQ7A will also clip.
It's whether or no you are happy with that loss on those days. Enphase don't have  higher output option available, so they have to try and justify it.
 

Offline EEVblog

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Re: EEVblog 1385 - 8kW Home Solar Power System EXPANSION
« Reply #38 on: April 09, 2021, 05:59:21 am »
DAVE have you actualy tested how much load your solar power system can produce in peak time,before you need to draw extra power from grid?

No because it's just insalled, but absolute peak with high soalr insolation I'd say about 4.13kW (max of the Enphase system) + maybe 2.8kW for the SMA system (was 3kW peak, but now not optimal) = approx 7kW. Maybe 6kW on an everage day.
Our consumption has peaked at about 8kW, but that's fairly rare.
 

Offline EEVblog

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Re: EEVblog 1385 - 8kW Home Solar Power System EXPANSION
« Reply #39 on: April 09, 2021, 06:00:51 am »
What stops a bank of micro-inverters from roasting a failed one also on that AC bus? There's no local disconnect or fuse that I can see.
I would be highly surprised if they didn't have  an internal fuse as a last-ditch protection measure- as it's potted, any internal fault would be unrepairable so the fuse doesn't need to be replaceable. 
In normal operation they will be actively monitoring everything throughout the AC cycle, so will be able to shut down in the event of any abnormal situation.

Yes, the IQ7 system has a measurment sample and processing time of 20us.
 
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Offline EEVblog

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Re: EEVblog 1385 - 8kW Home Solar Power System EXPANSION
« Reply #40 on: April 09, 2021, 06:04:21 am »
The Enphase consumption measurement problem got sorted today with an extra current transformer in parallel with the xisting one to compensate for the old SMA system production.
The SMA/Solar Analytics system is still giving wonky consumption results because it needs another CT as well to compensate for the production of the Enphase system!

The joys of having two different systems on the one circuit.
It's actually a rather interesting problem once you figure out what happening, will have to do a video on it.
 

Online bdunham7

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Re: EEVblog 1385 - 8kW Home Solar Power System EXPANSION
« Reply #41 on: April 09, 2021, 04:19:59 pm »
According to them, yes. But they have also admitted that my system will clip on high solar insolation days. Even the 340W output IQ7A will also clip.
It's whether or no you are happy with that loss on those days. Enphase don't have  higher output option available, so they have to try and justify it.

Why fixate on the clipping?  Go back and look at your own data and see how much total time your old system spent at more than 2.7kW.  Even a fairly small efficiency increase at other times, such as low light or partial shading, will make up for that. 

Also, even with 1kW/m2 insolation, it is unlikely your old panels actually produce their full STC-flash power.  You are basing your theory of solar production on your one example.  I can think of three possible explanations:

1) Your location has peak insolation well in excess of 1kW/m2 and/or it is actually quite cold in Sydney in December.  This seems unlikely, especially the latter.

2) Your power measurements are wrong.  I think this is unlikely as well, although 5% error wouldn't be unusual.

3) The accepted and published theories of solar panel energy production are wrong.  Or....

4) Your original panels had an STC flash power rating considerably higher than 250W.   I'm familiar with that line of panels because they came out right around the time I was shopping for panels.  I assume it was this one:

https://www.lg.com/us/business/solar-panels/lg-LG250S1C-G3

They made these, IIRC, in 250, 260 and 270W versions, which I presume were manufactured and then binned.  These ratings were not excessive or aggressive for a mono panel--I bought poly panels around the same time that were 240W.  Perhaps their process was better than anticipated and they down-binned some panels to meet orders for the 250W version.  Or perhaps they were worried about degradation and wanted to be conservative because of the production warranty.  Although I doubt you are likely to tear one off and send it for testing, I'd bet a small amount of money they would test well over 250W even now.
« Last Edit: April 09, 2021, 11:21:45 pm by bdunham7 »
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Offline EEVblog

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Re: EEVblog 1385 - 8kW Home Solar Power System EXPANSION
« Reply #42 on: April 11, 2021, 10:51:24 pm »
According to them, yes. But they have also admitted that my system will clip on high solar insolation days. Even the 340W output IQ7A will also clip.
It's whether or no you are happy with that loss on those days. Enphase don't have  higher output option available, so they have to try and justify it.

Why fixate on the clipping?  Go back and look at your own data and see how much total time your old system spent at more than 2.7kW.

I plan on doing exactly that.
BTW, I recall looking at measured insolation data at one point and I saw over 1000W/sqm in Sydney.
 

Online bdunham7

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Re: EEVblog 1385 - 8kW Home Solar Power System EXPANSION
« Reply #43 on: April 12, 2021, 02:28:25 am »
BTW, I recall looking at measured insolation data at one point and I saw over 1000W/sqm in Sydney.

It's entirely possible for that to happen on occasion, but keep in mind that unless it is cold, the -0.459%/K tempco of your panels will reduce the output by at least 10-12%.  One of the useful features of the Enphase system is that it gives you inverter temperature, which is a fairly decent proxy for panel temperature.

I think about 1050W/m2 is pretty much the absolute limit for clear sky--and that only under specific circumstances usually only found in northern climates.  However, if you have just the right combination of factors on a partly cloudy day, the limit is quite a bit higher.  Of course I don't own a pyranometer so I haven't measured anything directly myself, but published literature on this all seems to agree that 1kW/m2 is the normal maximum on clear days.

https://journals.ametsoc.org/view/journals/apme/47/11/2008jamc1861.1.xml

Edit:  I forgot to mention altitude as a factor, so there's that too.

« Last Edit: April 12, 2021, 02:36:08 am by bdunham7 »
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Offline EEVblog

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Re: EEVblog 1385 - 8kW Home Solar Power System EXPANSION
« Reply #44 on: April 12, 2021, 03:09:00 am »
BTW, I recall looking at measured insolation data at one point and I saw over 1000W/sqm in Sydney.

It's entirely possible for that to happen on occasion, but keep in mind that unless it is cold, the -0.459%/K tempco of your panels will reduce the output by at least 10-12%.  One of the useful features of the Enphase system is that it gives you inverter temperature, which is a fairly decent proxy for panel temperature.

I think about 1050W/m2 is pretty much the absolute limit for clear sky--and that only under specific circumstances usually only found in northern climates.  However, if you have just the right combination of factors on a partly cloudy day, the limit is quite a bit higher.  Of course I don't own a pyranometer so I haven't measured anything directly myself, but published literature on this all seems to agree that 1kW/m2 is the normal maximum on clear days.

https://journals.ametsoc.org/view/journals/apme/47/11/2008jamc1861.1.xml

Edit:  I forgot to mention altitude as a factor, so there's that too.

Here you go, the peak output power of the 3kW system histogramed over 1980 days.
My new 5kW system uses the same LG panels (but 370W vs 250W) in the exact same location. So I expect pretty close to the same peak output power of 5kW.
With 295W peak inverters, lets say 80% of the rated power at 1000W, so 4130W peak maximum possible, round to 80%.
Take the same 80% for old 3kW system (2400W) there are total of 769 days out of 1980 days where the peak output would exceed the inverters, or 38.8% of days. That's hardly "on occasion".
Data doesn't lie.
YMMV

 
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Online bdunham7

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Re: EEVblog 1385 - 8kW Home Solar Power System EXPANSION
« Reply #45 on: April 12, 2021, 04:14:51 am »
Take the same 80% for old 3kW system (2400W) there are total of 769 days out of 1980 days where the peak output would exceed the inverters, or 38.8% of days. That's hardly "on occasion".

"On occasion" referred to exceeding 100%, not 80%.  I'm at a similar latitudinal situation as you (inverted of course) and I routinely exceed 80%.  Nobody is denying that clipping will occur when the threshold is 80%. The question isn't 'how often', it is 'for how much time, and by how much".  According to Enphase's data, it amounts to 0.075% of your total energy production.  Their paper that is linked above,  and in your YouTube video comments, lays it all out, complete with the amount 'lost' due to clipping.

Enphase actually recommends a threshold as low as 75% (133% over-provisioning) and that only because your CEC has mandated that as a limit for some reason.    They even explicitly recommend the IQ7+ for your panels over the IQ7A and they explain why.  There are, in fact, good reasons to have systems with even higher overprovisioning because maximizing the usage of all available panel power is not the only valid objective, especially since panels have become so cheap.  For example, I could replace my panels with new LG ones like yours and new IQ7 inverters that are custom-configured to replace my old ones with a 225W max power output.  If you only looked at all the peak power I was 'wasting' due to clipping, it would seem a terrible idea.  It would be 165% over-provisioned and my clipping threshold would be 60%, which would horrify some.  But when you look at the fact that it would be a simple, easy retrofit that requires no new permitting or infrastructure, it's a great idea and would increase my power production tremendously.  Everyone will have their own situation, but these issues are common.  Avoiding clipping would lead to poorer system design in many cases, not to mention that SoCal Edison (my power company) really doesn't need a bunch of peak power in the middle of the day.

Some may object to the fact that a system like yours is commonly sold as a '5kW system', when in fact it can never produce that.  Up until now I've more or less agreed, but actually I'm not so sure that it is an invalid or even deceptive descriptor.  The '5kW' is a sort of sensitivity rating that describes how large a net you have for catching the sun.  Whether that is 25m2 at 20% efficiency or 50m2 at 10%, it is a valid way of comparing and the peak power issue has such a small effect on total energy production that it really only serves to confuse the issue.  IMO, the question is how much your electric bill would change if those inverters were 350W as opposed to 290.  If Enphase has given you good data the answer is 'not much'.  Then ask what the difference would be if you used 290W panels--the answer to that is 'a lot'.
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Offline EEVblog

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Re: EEVblog 1385 - 8kW Home Solar Power System EXPANSION
« Reply #46 on: April 12, 2021, 05:19:39 am »
Take the same 80% for old 3kW system (2400W) there are total of 769 days out of 1980 days where the peak output would exceed the inverters, or 38.8% of days. That's hardly "on occasion".
"On occasion" referred to exceeding 100%, not 80%.

In this case I am talking 100%, i.e. 14x295W=4.13kW
So 38% of days my inverters can be expected to clip.

As for the rest of your comments, yes, of course, and I've already shot a video on this, to be released shortly.
« Last Edit: April 12, 2021, 05:21:52 am by EEVblog »
 

Online bdunham7

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Re: EEVblog 1385 - 8kW Home Solar Power System EXPANSION
« Reply #47 on: April 12, 2021, 05:59:42 am »
In this case I am talking 100%, i.e. 14x295W=4.13kW
So 38% of days my inverters can be expected to clip.

OK, I was referring to exceeding 100% of the panel STC rating--that's an occasional event.  If you haven't read that link in my post, it refers to some interesting, and apparently not that rare, situations where irradiance can be much higher than 1kW/m2 for a short while--in one example they had 1832W/m2

Yes, I concur--according to your data, providing your new panels scale exactly as the nameplate rating (370:250), you will see some clipping on 38% of your days.  And with the Enphase monitoring system you'll be able to see it quite clearly.
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Offline EEVblog

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Re: EEVblog 1385 - 8kW Home Solar Power System EXPANSION
« Reply #48 on: April 12, 2021, 07:40:22 am »
In this case I am talking 100%, i.e. 14x295W=4.13kW
So 38% of days my inverters can be expected to clip.
OK, I was referring to exceeding 100% of the panel STC rating--that's an occasional event.  If you haven't read that link in my post, it refers to some interesting, and apparently not that rare, situations where irradiance can be much higher than 1kW/m2 for a short while--in one example they had 1832W/m2

Yes, the sun is a pesky thing.
My old 3kW system clipped occasionally too due to that.

Quote
Yes, I concur--according to your data, providing your new panels scale exactly as the nameplate rating (370:250), you will see some clipping on 38% of your days.  And with the Enphase monitoring system you'll be able to see it quite clearly.

I've already seen it clip, although Enphase claim it technically didn't.
4.172kW is greater than 4.13kW (14 x 295W), so yeah, I'd say it clipped in April.
Unfortunately I won't see it easily because I've now changed the system to show the total production from both systems.
« Last Edit: April 12, 2021, 08:01:16 am by EEVblog »
 

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Re: EEVblog 1385 - 8kW Home Solar Power System EXPANSION
« Reply #49 on: April 12, 2021, 11:50:06 am »
 


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